Placental insufficiency during pregnancy causes intrauterine growth restriction (IUGR) and predisposes offspring to Type 2 diabetes with reductions in functional ?-cell mass. Understanding the mechanism of this decrease in ?-cell mass in utero is essential to developing treatment strategies to prevent or reverse it. The complement system is an innate immune amplification system essential for host defense, inflammation and fetal survival, but excessive complement activation is associated with pregnancy complications including preeclampsia with IUGR. In the reduced uteroplacental perfusion pressure (RUPP) model of placental insufficiency in rat, blood flow to uteroplacental unit is mechanically disrupted at embryonic day (e)14, beginning of third trimester, resulting in placental ischemia, high blood pressure in dam and IUGR. Using this model, our published studies demonstrated ? cell area is reduced and increased apoptosis evident in e19 islet of growth restricted fetus, and increased maternal complement activation is critical for hypertension in RUPP dam. Our preliminary studies demonstrate decreased C3 and increased macrophage marker in e19 islets of RUPP offspring. Long-term goal: Determine therapeutic utility of manipulating complement or macrophages in utero or postnatally to mitigate reduced ? cell mass in IUGR offspring. Objective: Assess contribution of C3, C3a and macrophages to ? cell mass and survival in RUPP model. Central hypothesis: Placental ischemia results in decreased C3/C3a and change in macrophage numbers or M1/M2 phenotype in islets of offspring, ultimately leading to reduced ? cell mass and increased apoptosis. Aim 1: Determine whether decrease in C3 and/or C3a (Aim 1) or change in macrophage numbers or phenotype (Aim 2) are required for placental ischemia-induced reduction in ? cell mass and apoptosis in developing fetal pancreas. Time course of changes in C3, C3a, C3a receptor, and macrophages will be determined from e15 to 12 wk postnatal. Effect of decreasing C3 by siRNA or antagonizing C3aR in normal pregnancy (in utero or postnatally) on ? cell area or mass, apoptosis and macrophages will be determined. Conversely, ability of increasing C3a by administration of a C3aR agonist in RUPP offspring to rescue ? cell mass will be evaluated. The effect of fetal macrophage depletion using clodronate liposomes in utero or postnatally on complement, ? cell mass and apoptosis in fetal islets with and without placental ischemia will be assessed. This research is innovative because it is the first to examine the mechanistic role of complement in pancreatic development and its response to IUGR stress, and combines intradisciplinary expertise in islet biology with expertise in complement and RUPP IUGR model. This contribution will be significant because it will determine if targeting complement system or macrophages early in pancreatic development is a feasible therapeutic strategy for preserving pancreatic ? cell mass in the face of placental ischemia and thus preventing long term consequences in adulthood.